New 'Smart Skin' Could Make Prosthetics More Like Real Limbs

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New prosthetic skin that is warm and elastic like real skin, and
is packed with many different kinds of sensors, could one day
help people with prosthetic limbs regain their sense of touch,
researchers say.

In experiments, the researchers laminated "electronic skin" —
prosthetic skin embedded with electronics — onto a prosthetic
hand. They found that the skin could survive complex operations,
such as shaking hands, tapping keyboards, grasping baseballs,
holding hot or cold drinks, touching dry or wet diapers, and
touching other people. The electronic skin proved to be as
sensitive as expected to pressure, stretching, temperature and
dampness, successfully relaying data rapidly and reliably, the
researchers said.

The scientists included heating devices throughout the prosthetic
skin that could make it feel at least as warm as a person's body
temperature. Human skin is elastic, soft and warm, said study
co-author Dae-Hyeong Kim, a biomedical engineer at Seoul National
University in South Korea. "Our device has such properties," Kim
said. [ Bionic
Humans: Top 10 Technologies ]

In recent years, many research groups around the globe have been
developing bionic arms and legs that could help patients replace
lost limbs. Increasingly, scientists are looking for ways to
connect these
bionic limbs to human nervous systems, which could help
restore patients' sense of touch as well.

But replicating the sensory capabilities of real skin has proven
challenging. Recent efforts have aimed to develop smart
prosthetics embedded with sensors, but those sensors were
limited in either how sensitive they were, or how much data they
could measure.

The new skin is exceptionally sensitive, and can sense a wide
variety of data, such as information on temperature, humidity,
stretching and pressure, the researchers said. It could help lead
to "prosthetic devices for patients who lost arms, legs or skin,"
Kim added.

Typically, there are two factors that affect sensors' utility:
how sensitive they are, and their dynamic range — that is, the
range of data they can measure. "These two [factors] have an
offsetting relationship to each other — high sensitivity usually
results in a small range of measurements," Kim told Live Science.

One problem with prior attempts to make smart prosthetics was
that the sensors that were used were rigid, or semiflexible at
best. This meant they could only flex a certain amount before
fracturing, thus limiting the range of measurements they could
make.

In contrast, the new skin uses sensors made of
silicon ribbons that had a wavy, snake-like shape. This shape
lets the sensors withstand more strain — that is, stretching —
without breaking, and allows them to measure a greater range of
data.

The researchers also noted that the prosthetic skin can stretch
more on some parts of the body than on others. "Some parts of the
hand stretch only several percent, while other parts [stretch]
more than 20 percent," Kim said.

As such, the researchers matched the properties of the sensors on
the electronic skin to how much stretching it would experience
depending on which part of the body it covered. For instance, the
researchers made the prosthetic skin more sensitive for the areas
intended to cover parts of the hand where skin normally does not
stretch much. But for prosthetic skin that covers parts where the
skin would stretch a lot, they focused on improving the range of
data they could measure.

In addition, the researchers aimed to make their prosthetic skin
feel like real skin. "The feeling of artificial or prosthetic
arms to other people who interact with the wearer of these
devices is another important point to consider," Kim said.

The scientists also combined their electronic skin with an array
of stretchable platinum electrodes that would stimulate nerves to
relay sensor data to the brain. These electrodes were coated with
microscopic particles of cerium oxide to help control the
inflammation that such electrodes can trigger in the body. In
experiments with rats, the researchers showed this electrode
array could transmit data about the pressure of a touch to the
brain.

However, there are still safety concerns about this electrode,
such as the possibility that fractured electrodes could enter the
bloodstream and cause damage, the researchers said.

In the future, the scientists hope to conduct more animal trials
of their device. They detailed their findings online Dec. 9 in
the journal Nature Communications.